Antibodies have long been used in medical diagnosis, e.g., determining blood types, and in biological experimentation. With development of techniques of producing monoclonal antibodies which make it possible to obtain homogenous, highly specific antibodies, Kohler G. and Milstein, C.: (1975) Nature (London) 256 495-497the utility of antibodies has been greatly increased. Unlike antibody fractions which were previously available and which were actually heterogeneous mixtures of a number of antibody molecules reactive with a variety of antigenic determinants, the antibody molecules in a monoclonal antibody preparation all have the same idiotype and, consequently, generally are reactive with a single antigenic determinant ("epitope") or a group of structurally closely related antigenic determinants. Monoclonal antibodies are therefore much more precise probes for detecting the presence of a particular substance than were previous heterogeneous antibody fractions. The precise selectivity of monoclonal antibodies makes them particularly useful for diagnostic purposes and even as therapeutic agents against selected biological material, such as tumor cells. Monoclonal antibodies have been used to detect and isolate biological substances which were were previously unknown.
Generally, monoclonal antibodies are produced by immunizing an animal with a biological specimen or other foreign substance, obtaining antibody-producing cells from the animal, and fusing the antibody-producing cells with strains of neoplastic cells, e.g., tumor cells, to produce hybridomas which are isolated and cultured as monoclones. The monoclonal hybridomas may either be cultured in vitro or may be grown in vivo as ascites tumors in a host animal.
As understood in the art, all antibody-producing cells of an hybridoma culture derived from a single hybridoma cell produce antibodies of the same idiotype but, due to class-switching that might occur in some cells in the culture, possibly variable isotype.
As used herein, a "culture of an hybridoma" means a culture derived from a single hybridoma cell, i.e. a monoclonal hybridoma culture. "Culture," unless otherwise qualified, also means an ascites tumor, established with an aliquot of a culture of an hybridoma, and the associated ascites fluid. The "monoclonal antibodies" that are secreted by the cells of such a culture will have the same idiotype but might have different isotypes.
Not all of the hybridomas which result from fusing neoplastic cells with antibody-producing cells secrete antibody with desired idiotype, specific for the foreign substance or antigen used to immunize the animal from which the antibody-producing cells were taken, because not all of the antibody-producing cells from the immunized animal used in making the hybridomas produce antibody against that foreign substance or antigen. Indeed, the antigenic determinant of the foreign substance or antigen recognized by the monoclonal antibody from one such hybridoma culture might differ from the antigenic determinant of the same foreign substance or antigen recognized by the monoclonal antibody from another such hybridoma culture. Thus, it is necessary to screen antibody from an hybridoma culture, usually in combination with the culture medium or ascites fluid of the culture, for specificity by determining not only the ability of the antibody to recognize the foreign substance or antigen of interest but also its ability to recognize other biological materials that might occur in systems with which the antibody is to be used. While the necessity of characterizing the antibody of each clone by screening adds to the complexity of producing monoclonal antibodies, the wide variety of homogeneous antibodies which may be obtained gives investigators a number of very precise tools to map the structure and development of somatic cells.